The present invention relates to dyeing of fibers and more particularly to reactively dyed fibers in which a chromophore is chemically linked to sites on the fiber.
Dyes are retained in fibers by physical adsorption, salt or metal-complex formation, solution, entrapment, or the formation of covalent chemical bonds. Physical adsorption and solution, in which the dye is partitioned between the fiber and the surrounding aqueous phase, are equilibrium processes, and only by very careful selection of the dyes used, can good washfastness properties be achieved. Salt and metal complex formation are also equilibrium reactions and, though generally the retention of the dye is favored more than in physical adsorption, washfastness may still present a problem. The dyes that are held by entrapment (azoics, vats and sulfurs) are virtually insoluble in water and show excellent fastness to washing, but have other disadvantages. They are, for example, difficult and expensive to apply; loose dye, which is not easily washed off, may be deposited on the surface, resulting in low fastness to rubbing (crockfastness), and the final shade of the dyeing does not develop until completion of the whole dyeing cycle and aftertreatments.
Chemical bonding of dye to fiber for fixation of dye was recognized as early as 1895. The reactive dye systems presently available require that the dyes contain a functional group capable of forming a covalent chemical bond with the fiber.
Fiber-reactive dyes are employed quite widely in coloring cellulosics and proteinaceous fibers. They, of course, exhibit excellent washfastness, resistance to rubbing, tinctorial powers, ease of application and leveling. The latter quality is a measure of uniformity and most important for long dye runs and color matching. The reaction of the dye with cellulosic fibers is basically an etherification or esterification reaction and is broadly represented as: ##STR1## EQU Dye-SO.sub.2 CH.sub.2 CH.sub.2 OH+Cell-OH.fwdarw.Dye-SO.sub.2 CH.sub.2 CH.sub.2 O-Cell (II)
Reactive dyes of Type I are labile halides, and as such they are by nature of limited stability in storage and difficult to work with. Their reactions are generally effected under alkaline conditions. There are few presently available reactive dye systems which operate well under acidic conditions. An acidic system is often desirable in the dyeing of mixed fabrics such as cotton blends with polyester, wool or nylon, the latter two fibers being dyeable by acid dyes. However, acid dyes generally have no affinity for cellulose and usually only find use in dyeing of proteinaceous fibers.
The American Cyanamid Company has published a booklet entitled "Cyanamide", which sets forth a considerable number of reactions of cyanamide and dicyandiamide. Page 32 of this booklet indicates that cyanamide was long known to be a dehydrating agent when warmed in anhydrous formic acid or when used in the esterification of lactic or salicylic acid with absolute ethanol. Note Pratorius-Seidler, G.,J. prakt. Chem [2] 21, 129-50 (1880); C. 1880, 245. A number of papers have investigated the reaction of cyanamide with carboxylic acids, and have proposed a mechanism wherein the acid is converted to the anhydride by interaction with cyanamide, with formation of urea. Subsequently the urea is acylated by the anhydride to produce a ureide, which at elevated temperatures interacts with the acid to produce an amide.
The use of cyanamide and phosphoric acid to impart flame retardant properties to cotton and other cellulosic fabrics is well known to the art. For instance, O'Brien, "Cyanamide Based Durable Flame-Retardant Finish for Cotton", Textile Research Journal, March, 1968, pp. 256-266 indicates, at page 265, that the reaction of cyanamide and phosphoric acid with cellulose results in a cross-linking of cellulose molecules. From the properties of the resulting product, it is suggested that the cross-linked cellulose is some type of dicellulose phosphate ester.
Copending, commonly assigned application Ser. No. 534,349, filed Dec. 18, 1974, to Swidler and Sanderson, discloses the use of cyanamide compounds, such as cyanamide and dicyandiamide, to aid in the reactive dyeing of substrates containing certain types of active hydrogen atoms, including cellulosic fibers, with phosphorus-containing dyes, such as dyes containing phosphonic acid groups, or salts thereof.
U.S. Pat. No. 3,535,308 discloses a process for preparing organic esters of polyhydroxylic polymers. These organic esters are indicated to have various uses, including application to textiles, as presented in more detail in, for example, Ott et al, Cellulose and Cellulose Derivatives, Vol. V, Part II, pp. 763-820. The polymers are prepared by contacting a polyhydroxylic polymer containing esterifiable hydroxyl groups with cyanamide or cyanamide salts and a carboxylic acid for a time sufficient to impregnate the polymer with the cyanamide and the acid. Thereafter the impregnated polymer is heated for a time sufficient to react the components to produce the partially esterified polymer. The degree of esterification is indicated to depend upon many different factors, and it is indicated that polymers containing as many as one ester grouping for every 10-30 esterifiable hydroxyl groups have been prepared.